Animal locomotion requires the coordinated firing of motor neurons that trigger the contraction of muscles in the appendages, such as the legs. In addition, coordination requires feedback from sensory neurons located in the appendages. To understand how functional motor neuron circuits form, this project will investigate the development and function of the motor circuit used by the adult fruit fly for walking. The combinatorial transcription factor code required to give each motor neuron its particular identity will be deciphered using both novel genetic and molecular biology approaches. Once identified, the consequences on walking of perturbing small numbers of motor neurons will be analyzed. Finally, the role of sensory feedback from mechanosensory organs in the legs will be characterized. Together, these studies will lay the ground work for a new model genetic system for studying motor circuits in a genetically tractable animal that, unlike its larval counterpart, uses appendages for locomotion.